Chemistry Basics: Elements, Molecules, and Carbohydrates

Elements and Molecules

• An element is a pure substance with specific physical and chemical properties.
• The smallest unit of matter that retains the chemical properties of an element is an atom.
• Intra-molecular forces are responsible for holding atoms within a molecule together.

Carbohydrates

• Carbohydrates consist of carbon, hydrogen, and oxygen atoms.
• A monosaccharide has a 5-carbon structure (e.g., ribose).
• Disaccharides are composed of two monosaccharides linked together.
• Glycogen is an energy storage molecule in humans, composed of alpha-bonded polysaccharides.

Proteins

• Proteins are composed of carbon, hydrogen, oxygen, and nitrogen atoms.
• Amino acids combine to form polypeptides.
• The primary structure of a protein refers to the sequence of amino acids.
• The secondary structure of a protein is influenced by intermolecular forces due to hydrogen bonding between the polypeptide backbone.
• Tertiary structure involves the creation of hydrophobic or hydrophilic spaces through interactions between R-groups.
• Quaternary structure involves the assembly of multiple polypeptide chains to form a single protein.
• Protein denaturation involves the loss of protein function and higher order structures, but the primary structure remains unaffected.

Enzymes

• Enzymes act as biological catalysts, binding to substrates and converting them into products.
• Enzymes lower the activation energy of a reaction, increasing the reaction rate.
• The transition state is the unstable intermediate state between reactants and products.
• Cofactors are non-protein molecules that aid enzyme reactions.
• Competitive inhibitors compete with the substrate for active site binding, increasing Km while Vmax remains the same.

Cellulose and Chitin

• Cellulose is a structural component in plant cell walls, composed of beta-bonded polysaccharides.
• Cellulose is arranged in linear strands packed rigidly in parallel.
• Chitin is a structural component in fungi cell walls and insect exoskeletons.

Lipids

• Lipids are hydrophobic due to their long hydrocarbon tails.
• Triacylglycerol molecules are composed of a glycerol backbone and three fatty acids connected by ester linkages.
• Saturated fatty acids solidify at room temperature due to the lack of double bonds, leading to tight packing.
• Cis-unsaturated fatty acids have kinks in their hydrocarbon tails, preventing tight packing.
• Phospholipids are composed of a glycerol backbone, one phosphate group, and two fatty acids.
• Phospholipids arrange themselves into a lipid bilayer due to their amphipathic nature.

Glycogen and Cellulose

• Glycogen is an energy storage molecule in humans, composed of alpha-bonded polysaccharides.
• Cellulose is a structural component in plant cell walls, composed of beta-bonded polysaccharides.
• Chitin is a structural component in fungi cell walls and insect exoskeletons.### Lipids
• Lipids have an amphipathic nature, meaning they have both hydrophobic and hydrophilic regions.
• Cholesterol is a precursor to steroid hormones.
• Lipoproteins transport lipid molecules in the bloodstream.
• Low-density lipoproteins (LDLs) deliver cholesterol to peripheral tissues.
• High-density lipoproteins (HDLs) transport cholesterol to the liver for bile production.
• Waxes are used as hydrophobic protective coatings.
• Carotenoids are lipids that contain conjugated double bonds and six-membered rings, and they act primarily as pigments.

Nucleic Acids

• Nucleic acids are composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus atoms.
• The basic composition of nucleosides is a 5-carbon sugar and a nitrogenous base.
• Nucleic acids are composed of nucleotide monomers.
• Phosphodiester bonds link nucleotides with a 5' end and a 3' end.
• Nucleic acid polymerization occurs through the addition of nucleoside triphosphates to the 3' end of the sugar-phosphate backbone.
• DNA forms an antiparallel double helix with complementary base pairing.
• Adenine and thymine interact through 2 hydrogen bonds.
• RNA is single-stranded and contains uracil, which binds to adenine.

Carbohydrates

• Glycogen is a polysaccharide that serves as an energy storage molecule in humans.
• Glycogen is composed of alpha-bonded glucose units.
• Cellulose is a beta-bonded polysaccharide that provides structural support in plant cell walls.
• Chitin is a polysaccharide that is found in fungi cell walls and insect exoskeletons.

Proteins

• Proteins are formed through the process of translation, where mRNA is used to synthesize a protein.
• Hydrogen bonds contribute to the secondary structure of proteins.
• Ribozymes are RNA molecules that have catalytic properties and exhibit lower activation energy.
• Enzymes are highly efficient due to their high specificity constant.
• Phospholipids are differentiated from glycolipids by the presence of a phosphate head group.

Cells

• Cells originate from pre-existing cells through cell division, according to the modern cell theory.
• The central dogma of genetics states that genetic information flows from DNA to RNA to proteins.
• RNA played a central role in the origin of life on Earth, according to the RNA world hypothesis.

Chemical Reactions

• Dehydration reactions form glycosidic bonds between monosaccharides.
• Hydrolysis reactions involve the breaking of a covalent bond by adding water.
• Combustion reactions involve the reaction of a hydrocarbon with oxygen, producing CO2 and H2O.
• Empirical formulas provide the most-reduced whole number ratio of each atom in a compound.